Fluid spring



April 27, 1965 E. F. HEISER 3,180,534

FLUID SPRING Filed Nov. 1. 1961 I ax 5 R i 1/ 1/ 1111 I I IIJ III 7/ -62 l7 I w 1 I '72 INVENTOR. ELMER E HE ISER ATTORNEYS 3,180,634 FLUID SPRING Elmer F. Heiser, Parma Heights, Ohio, assignor toPrecision Products, Iuc.,'- Cleveland, Ohio, a corporation of Ohio . Filed Nov. 1, 1961, SenNo. 149,405

10 Claims. (Cl. 267-1) The present invention relates to a piston-cylinder structure and, particularly, to a piston and cylinder structure ,to be used as a hydraulic or pneumatic spring.

Piston-cylinder structures are commonly used with :relatively movable first and second metal forming dies in ,the place of springs to provide a biasing or cushioning force on one-of the dies or a pressure pad normally associated with the dies. A pressure pad is used to hold the work against one of the dies, for example, the first die,

and the cylinder of the fluid pressurespring is normally fixed to the other or second die and a piston or ram extends from the cylinder to engage the pressure pad to yieldably-urge the seconddie and pad apart, thereby urging the latter towardthe first dies The area of con .tact between the piston or ram andthe pressure pad vtransmits a high pressure and once the pad and piston ,or ram are'in engagement, the point of contact will tend .to move along the .line of movement of the relatively movable dies when the dies move toward each other.

The; piston-cylinder structures heretofore used as fluid pressure springs have been subject to wear and therefore have. had a short life. It has been found that regardless of: the accuracy of the mounting'of the fluid pressure spring, it is almost impossible, as a practical matter, to

assure that the movement of the aforementioned point of contact is along the axis of the piston-cylinder structure, that is, the axis of the piston cylinder structure will generally be angularly disposed, at least to a small extent, with respect'to the line of movement of the point of contact. It has been observed that this is the cause ;ofwear in the cylinder since the lateral forces on the piston side load the piston and press it against the cylinder wall with suflicient force to break down the normal lubrication between thepiston and cylinder. As a result,

'a direct metalto metal .scrubbingiaction takes place which destroys the close fitbetween the piston and cylinder surfaces.

Accordingly,'the principal object of the present inf; vention is the provision of a new and improved fluid" pressure spring of the piston-cylinder type which is not subject to the above mentionejdIfscrubbing action and therefore has a longer useful life than known. fluid pressure'springsr H Another object of the present invention is the provision of anew and improved piston-cylinder structure wherein thepiston head is associated with the'piston rod in a manner' which permits the piston rod to move 'uni- V piston rod is not connected to'the piston head\but is provided with .a surfacevwhich abuts a complementary surface on the piston head, which surfaces are held in engagement during installation .of the spring and main- 7 tained properly aligned with respect to each other once the spring is installed. i M p V Additionally, this invention ,provides a fluid spring of the above noted type wherein the piston rod has an end cap for. engaging one of the members between whichthe fluid spring is mounted and a spring means for'biasing the end cap into an extended position and when the end United States Patent imovable therewith.

ice

cap is in engagement with the aforementioned member to bias the piston rod 'into engagement with the piston head. A

Further objects and advantages of the present invention will be apparent from the following detailed description of a preferred embodiment thereof made with reference to the accompanying drawings in which: 7

FIG. 1 is a sectional view of an apparatus embodying the present invention; and

FIG. 2 is a sectional view of a modified piston head and rod which may be used in the apparatus of FIG. 1.

In FIG. 1 of thedrawings the present invention is shown applied to a sheet stamping press A having a fixed die 10, which receives a sheet S to be worked upon, and a movable die 11 which cooperates with the fixed die 10 to bend the edge of the sheet S. The movable die 11 has a work holder 12 and a fluid spring B mounted thereon and The work holder 12 comprises a support plate 14 and work engaging portions 15 depending therefrom." The 'work engaging portions 15 thereof project below the die 11 and engage the sheet S to hold it against die 11 before the Work engaging portion of die'11 engages the sheet. Continued movementof die 11 after work holder 12, engages the sheet causes the work holder to movefrelative to die 11. The work holder is slidably mounted on die 11 to, effect the above mentioned relative movement by support and guide means comprising a projecting rod 16 which is secured to the movable die 11 and extends through a bore 17 in the support plate 14. The side of the support plate 14 opposite the side facing die 11 is counter-bored at 19, thus providing a shoulder 22 which cooperates with a head 23 on the end of rod 16 to hold the work holder on the rod 16.

The fluid spring B is mounted in an opening in the die 11 in a conventional manner and includes asuitable hy-' draulic cylinder 30 having a pressure connection 32 secured at one end thereof and a cylinder head 33 at the other end thereof. A piston head 34 is movable in the cylinder 30 and engages a piston rod 35 which extends 45, one end of which is provided with a groove 47 for receipt of a split ring] 48 and the other end is provided with a radially projecting skirt portion 56 which encircles the cup member 45. Thefend of the cup member from which the skirt 50 projects has anaxially extending here 51 therein,.the bottom of which is provided with a "concave recess 52. Bearings 53 and suitable packing 54 encircle the cup member 45 and are positioned between the split ring 48 and skirt portions 50. and engage the interior surface of cylinder 30 to guide the movement thereof within the cylinder 3i). The bearings 53 may be of any-suitable nature and may be metallic with self lubricating properties or plastic. Preferably, they are phenolic bearings. V

The piston rod 35 comprises a cylindrical body portion having an axially extendingrod portion 61 projecting from one end thereofand a bore 62 in the other end thereof. The rod portion 61 has a spherical bearing surface 63 on the free end thereof which is com- 'plementary to the spherically concave recess 52 in the bottom of the bore 51 in the piston head. The rod portion 61 is also provided with a circumferential groove 64 adjacent its free end which receives a resilient circular holding element 65.

the atmosphere.

The piston rod 35 and piston head 34 are associated in a manner which permits free universal pivotal movement of the piston rod and the piston head with respect to each other. The rod portion 61 of the piston rod is positioned in the bore 51 of the cup member 45 with the spherical bearing surface 63 on the end thereof abutting the concave recess 52 at the bottom of bore 51. This arrangement provides a universal connecting means between the piston rod and piston head permitting free pivotal movement therebetween.

The surfaces 52, 63 are held in abutment, at least in part, by the resilient holding element 65 which frictionally engages the inner surface of the bore 51 and functions to hold the piston rod in position in the bore during installation thereof and any other time when the pistonrod is otherwise free to fall out of the bore 51. The holding element 65 also centers the piston rod in the bore 51' A circumferential groove .74 is provided in the projecting portion 71, near the end thereof which engages the spring means 73 for receipt of a resilient retaining element 75 which frictionally engages the interior surface of the bore 62 to hold the end cap 70 in position with respect to the body portion 60 of the piston rod 35, the spring 73 being extendable to the position which it naturally tends to assume with the portion 71 disposed in the bore 62. The bore 62 and the retaining element 75 are associated in such a manner that the space between the end of portion 71 in the bore and the bottom of the bore is vented to The spring means 73, it will benoted, will normally bias the end cap 70 into an extended posi tion, but will, if the end cap is restrained and the spring 73 compressed, urge the rodportion'l into engagement ing the cooperating surfaces 52, 63 in abutting relation. In accordance with the preferred embodiment of thepresent invention, the maximum spacing between thecylinder 3i and the pad 12 is such that the'spring 73 is maintained under compression even when the pad is separated from the die It and sheet S. This assures that the surfaces 52, 63 do not separate during normal operation. a

The cylinder head 33, which has opening 36 through which the piston rod 35 extends, is constructed to accommodate the aforementioned free pivotal movement between the piston rod 35 and piston head 34 and provides a'positive stop for the piston head to limit the. movement thereof. The cylinderhead 33 is secured to the cylinder 30 in such a manner that it can accept the full force of ,the piston head 34 at maximum fluid pressure and" thus prevents the piston from blowing out if pressure is admitted prior to installation. 7

The cylinder head 33, through which openingfid extends, is provided with two circular ledges 81, 82, around opening 36, by counterbores .83, 84, respectively. A resilient centering guide 85 is positioned to engage ledge 81 movement by the piston rod compressesthe resilient mern ber 87. p a

The resilient centering guide 85 is held in position on ledge 81 by a circular retaining member 88-which with the cup member of the piston head, thereby hold- V 4,, engages. ledge Bland is secured in position: by a split ring 99 which is received in a groove 91 on the inner surface of \counterbore 84.

It is apparent upon reference to FIG. 1 that when the fluid spring is installed the pistonrod end cap 70 engages a. surface of the work holding member 12 opposite the side from which work engaging portions 15 extend.

.In such'a position the spring means 73 functions, as aforementioned, to bias the, pistonbrod:35 into engagement 'pad when the dies are open. Evenif the necessary dimensions andtolerances were initially provided, wear would soon destroy the close dimensioning and the surfaces would separate. "A separation of the abutting surfaces. 52, 63 would cause these surfaces to be'moved together and collide at a high. velocity upon relative movement between-the work holder and piston rod 35 on die closing. Since these surfaces are relatively, small, the force'per square inch of surfacearea, in such an event, would bequite large and damage could easily result.

In the preferred embodiment, wherein spring means 731's provided, as thework holder'12 slides relative to rod 14 and die 11, the end cap 70 will be moved against the end of body portion 60 and thereby force the'piston rod to move the piston head, Sincethe area of contact between the end cap 70;and.the end of portion 60 is relatively large, the possibility of'damagecaused by the impact of end cap 70 engaging body portion 6t)v is considerably'lessthan if the surfaces 52 and 63 were to collide. The piston rod, as it is movedbyP engagement of end'cap 70 with the work holderxl z, will tend to move along the line of movement; of the work ho1de'r 12 while the piston head 34 will leIldIO move along the center line of the cylinder 30 which; as aforementioned, are usually misaligned,thereby causing a slight pivoting motion between the piston'rod-and piston'head, at? the concave surface 52 and convex surface 63 which are in engagement. This pivoting motion'results in-a change of angularity of the piston rod relative to the axis of the bore of cylinder 30 and a rocking will occur about thecurved surface 72a 'of the endicap 72.which is in engagement with the workholder 14. It is apparent that the concave and convex surfaces 52'and' 63, respectively, and the end cap structure provides-a piston rod having opposite end portions which. are supportedjforlimiteduniversal pivotal 'movement;

Themodified pistonhead and rod arrangement shown v in FIG. 2' comprises apistonhead which is identical to the piston head .describedabove having a cup member 45 with a groove 47 atone end, QSkllt 50- at the otherend,

and a bore 51 .havinga concave-recess 52 at the bottom thereof. Thepiston rod, how'ever,'is modified: and includes abodyportion'94 having a rod portion 95 extend ing fromone'end thereof into the bore 51'and secured therein hiya retaining element 96 positioned in a groove 97 in the rod portion 95.. The end of the rod portion 95 in bore 51 has a concave recess 98 similar to the recess 52in the bore-51. A circularballmember 99 having a spherical surface which corresponds to the recesses 52 and 98 is positioned so that aportion of the surface there.

scope,'but includes all modifications, changes and adaptations coming withinthe terms of the claims hereof.

Having described my invention, I claim:

1. In a device for use with relatively movable first and second members, a cylinder adapted to be fixed in said first member, a piston head movable in said cylinder and biased in a first direction by a biasing force in said cylinder, a piston rod having one end in abutting engagement with saidfpiston head, said engagement consisting of cooperating concave and convex surfaces on the piston head and piston rod, an end cap slidably mounted on the other end of said piston rod opposite said one end to engage said second member, and spring means positioned between said end cap and said second end of said piston rod to urge said concave and convex surfaces into intimate contact when said end cap is in engagement with saidsecond member.

2. In a device for use with a movable member as described in claim 1 wherein said end cap upon relative movment of said first and second members in a direction opposite said first direction is moved into engagement with said second end of said piston rod and the area of contact'between said end cap and second end of said piston rod is greater than the area of contact between said concave and convex surfaces.

3. A device for use with relatively movable first and second members, a cylinder adapted to be fixed on said first member, a piston head having a bore therein movable in said cylinder, a concave recess at the bottom of said bore, a piston rod extending into said bore and having a convex surface on one end thereof in engagement with said concave surface and a second bore in the other end thereof, resilient means frictionally engaging the inner surface of said first bore and the surface of said rod for centering said rod in said bore, an end cap slidably mounted on said other end of said piston rod to engage said second member, and spring means positioned in said second bore in engagement with the bottom of said bore and said end cap to urge said end cap in extended position and to urge said concave and convex surfaces into intimate contact when said end cap is engaged with said second member.

4. In a device of the class described, a cylinder, a piston head movable in said cylinder, a piston rod, cooperating concave and convex surfaces on one end of said piston rod and said piston head in abutting relation for permitting relative pivotal movement between said piston head and piston rod, a'bore in the second end of said piston rod, a piston rod end cap having a projection thereon extending into said'bore, and spring means positioned in said bore between the bottom thereofand the end of said projection for biasing said end cap outwardly of said bore and for urging said concave and convex surfaces into firm engagement when said end cap is limited against movement by said spring means.

5. A device as defined in claim 4 wherein said end cap upon compression of said spring means engages the end of said piston rod having the bore therein and the area of contact between saidend cap and said second end of said piston rod is greater than the area of contact between said concave and convex surfaces.

6. In a device of the class described, a cylinder, a cylinder head secured to one end of said cylinder and having an opening therethrough, a piston head movable in said cylinder, a bore in said piston head, a concave recess at the bottom of said bore, a piston rod extending through said opening and into said bore, a convex surface on the end of said piston rod in said bore for engaging said concave surface at the bottom of said bore, resilient means in said bore engaging the inner surface of said bore and the surface of said piston rod for centering said piston rod in said bore, a resilient centering guide in said opening for centering said piston rod in said opening to align said piston rod with respect to said bore a 6 and being compressed upon pivotal movement between said piston head and said piston rod.

7. In a device of the class described, a cylinder, a pressure connection secured to one end of said cylinder for connecting said cylinder to a supply of fluid under pressure, a cylinder head secured to the other endof said cylinder and having an openingtherethrough, a piston head movable in said cylinder, a first bore in said piston head, a concave recess at the bottom of said first bore, a piston rod extending throughsaid opening'and into said first bore, a convex surface on theend of said piston rod in said first bore for engaging said concave surface at the bottom of said bore, resilient means in said first bore and engaging said piston rod for fcentering said piston rod and frictionally holding said piston rod in said first bore,

a resilient centering guide in said 'opening for centering said piston rod and supporting said piston rod in said opening and being yieldable upon the application of external forces to said piston rod, a second bore in the end of said piston rod opposite the end having said spherical surface, a piston rod end cap having a projection thereon extending into said second bore, means in said second bore frictionally engaging said projection and the inner surface of said second bore for holding said end cap in said second bore, and a resilient compression member positioned between the bottom of said second bore and the end of said projection for biasing said end cap outwardly of said bore and for urging said concave and convex surfaces into firm engagement when said end cap is limited against movement by said resilient member.

8. In a device of the class described, a cylinder, piston means movable in said cylinder and including a piston headhaving a first surface thereon and a piston rod extending outwardly of said cylinder and having a second surface in abutting engagement with said first surface and movable relative thereto, a bore in the outer end of said piston rod extending in the direction of the length of said piston rod, a piston rod end cap movable lengthwise in said bore and having a portion extending outwardly of said bore, and spring means positioned in saidbore between the bottom thereof and said end cap and ing said first and second surfaces into firm engagement when said end cap is limited against movement by said s rin means. 45 P g 9. In a device of the class described, a cylinder having an axial bore therein, a cylinder head secured to one end of said cylinder and having an opening therethrough, a piston head movable axially in said cylinder bore, a piston rod extending from said piston head through said opening, pivot means between said piston rod and cylinder allowing movement of said piston rod in a direction generally transverse to the axis of said cylinder, and guide means positioned in said opening in said cylinder head and engaging said piston rod and movable by said piston rod upon movement of said piston rod transverse to the axis of said cylinder, said guide means comprising a substantially rigid guide member encircling said piston rod and a resilient member encircling said rigid guide member and positioned in said cylinderhead to be compressed upon movement of said rigid guide member transverse to the axis of said cylinder by said'piston rod.

10. In a device of the class described, a cylinder having an axial bore therein, a cylinder head secured to, one end of said cylinder and having an opening therethrough, a piston head movable axially in said cylinder bore, a piston rod extending from said piston head through said opening, pivot means between said piston rod and cylinder allowing movement of said piston rod in a direction generally transverse to the axis of said cylinder, and guide means positioned in said opening in said cylinder head and engaging said piston rod and movable by said piston rod upon movement of said piston rod transverse to the axis of said cylinder, said guide means comprising a rigid piston rod guide member positioned in said opening in said cylinder head and closely engaging said piston rod and movable by said piston rod transverse to the axis of said cylinder, and means includinga resilient element between said guide member and saidcylinder head for retaining said guide member in position and yieldably holding said guide member against movement transverse to the axis of said cylinder and yielding upon movement of said piston rod transverse to the axis of said cylinder.

Refierences Cited by the Examiner UNITED STATES PATENTS 98,839 1/70 Ball 78-40 1,487,177 3/24 Nygaard. 1,575,847 3/26 King et a1.

' 2,122,871 7/38 Sane 267-1 X 2,255,181; 9/41 Newton 267-64 2,279,447 4/42 Cowey "2674-64 X 2,426,155 8/47 Rode. g

References Cited by the Applicant 10' UNITED STATES PATENTS Re. 24,440 3/58 Groen.

2,466,428 4/49 Hufierd. 7 73,033,578 5/62 Kellogg: 5 ARTH R L. LA POINT, Prima i y Ex aminer.

RICHARD A. DOUGLAS, ROBERT C, RIORJDON,

Examiners.

earn; 

1. IN A DEVICE FOR USE WITH RELATIVELY MOVABLE FIRST AND SECOND MEMBER, A CYLINDER ADAPTED TO BE FIXED IN SAID FIRST MEMBER, A PISTON HEAD MOVABLE IN SAID CYLINDER AND BIASED IN A FIRST DIRECTION BY A BIASING FORCE IN SAID CYLINDER, A PISTON ROD HAVING ONE END IN ABUTTING ENGAGEMENT WITH SAID PISTON ROD HEAD, AND ENGAGEMENT CONSISTING OF COOPERATING CONCAVE AND CONVEX SURFACES ON THE PISTON HEAD AND PISTON ROD, AND END CAP SLIDABLY MOUNTED ON THE OTHER END OF SAID PISTON ROD OPPOSITE SAID ONE END TO ENGAGE SAID SECOND MEMBER, AND SPRING MEANS POSITIONED BETWEEN SAID END CAP AND SAID SECOND END OF SAID PISTON ROD TO URGE SAID CONCAVE AND CONVEX SURFACES INTO INTIMATE CONTACT WHEN SAID END CAP IS IN ENGAGEMENT WITH SAID SECOND MEMBER. 